1. Field of the Invention
The present invention relates to an angular velocity sensor suitable for detecting the angular velocity of a rotating body and the like.
2. Description of the Related Art
A first known angular velocity sensor (such as disclosed in Japanese Unexamined Patent Application Publication No. 5-312576) includes a substrate, a first vibrator supported on the substrate by a first support beam and vibratable in parallel to the substrate, a second vibrator supported by a second support beam parallel to the first vibrator and vibratable in a direction orthogonal to the vibrating direction of said first vibrator, vibration generating means for vibrating the first vibrator parallel to said substrate, and angular velocity detecting means for detecting the amount of displacement of said second vibrator as an angular velocity.
This conventional angular velocity sensor has three orthogonal axes, an X-axis, a Y-axis and a Z-axis. When an angular velocity around the X-axis direction is applied to the sensor, while a constant vibration is applied to, for example, the X-axis, the second vibrator is displaced in the Y-axis direction by a Coriolis force. Then, the angular velocity detecting means detects the displacement in the Y-axis direction of the second vibrator by the Coriolis force as variations of piezoelectric resistance, electrostatic capacitance and the like, and thereby the angular velocity is detected.
Further, a second conventional angular velocity sensor is known which includes a sensor, a movable part provided on a substrate by a support beam so as to be displaceable in the X-axis direction and in the Y-axis direction, vibration generating means for vibrating the movable part in the X-axis direction, angular velocity detecting means for, when an angular velocity around the Z-axis is applied while the movable part is vibrated in the X-axis direction, detecting the displacement of the movable part by a Coriolis force in the Y-axis direction, and displacement detecting means for detecting the amount of displacement when the movable part is displaced in the X-direction by the vibration generating means. An example of such a conventional angular velocity sensor is disclosed in European patent Publication No. EP0862048A2.
In the second conventional angular velocity sensor, the displacement detecting means includes electrodes provided between the movable part and the substrate, and the amount of displacement when the movable part is displaced in the X-axis direction is detected as a variation of electrostatic capacitance between these electrodes. Therefore, since the second conventional angular velocity sensor detects the displacement of the movable part in the Y-axis direction using the angular velocity detecting means, and detects the vibration of the movable part in the X-axis direction using the displacement detecting means, it is possible to detect a driving state when the movable part vibrates in the X-axis direction and then it is possible to control the vibration generating means to maintain a constant amplitude and to vibrate the movable part in the X-direction in a resonant state. As a result, since it is possible to vibrate the movable part in a resonant state, it is possible to detect a stable output (amount of displacement) of the movable part in the Y-axis direction.
In the first conventional angular velocity sensor disclosed in Japanese Unexamined Patent Application Publication No. 5-312576, it is possible to detect a stable output in the Y-axis direction when the frequency of vibration is always in a resonant state and the amplitude is constant while the first vibrator vibrates in the X-axis direction. However, in practice, when the first vibrator vibrates, the frequency and the amplitude vary due to deterioration over time, manufacturing errors and the like. In this case, there is a problem in that the output of the second vibrator becomes unstable and the detection sensitivity of the angular velocity deteriorates substantially.
The second conventional angular velocity sensor disclosed in European Patent Publication No. EP 0862048A2 detects the amplitude of the movable part in the X-axis direction by the displacement detecting means and controls the vibration generating means so that the amplitude becomes constant.
However, in the second conventional angular velocity sensor, the displacement detecting means is the electrode provided between the movable part and the substrate. However, the movable part is displaceable in two axial directions; therefore, a situation arises in which the electrodes of the displacement detecting means positioned approximately in parallel are inclined in accordance with the displacement of the movable part. Therefore, since the electrostatic capacitance between the electrodes provided between the movable part and the substrate varies by this inclination of the electrodes, there is a problem in that the displacement of the movable part in the X-axis direction can not be detected accurately.
Accordingly, the object of the present invention is to provide an angular velocity sensor which is capable of accurately detecting a vibration state by the vibration generating means and capable of always vibrating the first vibrator at a constant amplitude.
To achieve the foregoing and other objects, the present invention provides an angular velocity sensor including a substrate, a first vibrator supported by a first support beam on said substrate and arranged such as to be vibratable parallel to the substrate, a second vibrator supported by a second support beam parallel to said first vibrator and arranged such as to be vibratable in a direction orthogonal to the vibrating direction of said first vibrator, vibration generating means for vibrating the first vibrator parallel to said substrate, and angular velocity detecting means for detecting the amount of displacement of the second vibrator as an angular velocity.
In accordance with a first aspect of the invention, monitor means is provided between the substrate and the first vibrator for monitoring the amount of displacement of said first vibrator when it is vibrated by the vibration generating means.
With this configuration, when a driving signal is input into the vibration generating means from the outside, the first vibrator and the second vibrator vibrate parallel to the substrate, and when an angular velocity is applied around an axis orthogonal to the substrate in this state, the second vibrator is displaced parallel to the substrate and in a direction orthogonal to the vibration direction due to a Coriolis force.
In this case, the angular velocity detecting means detects a displacement in a direction orthogonal to the vibration direction generated in the second vibrator due to the Coriolis force when an angular velocity is applied around an axis orthogonal to the substrate while the first vibrator and the second vibrator vibrate parallel to the substrate. Also, the vibration-state monitor means detects the displacement of the first vibrator vibrating parallel to the substrate due to the vibration generating means.
With this configuration, the vibration of the second vibrator can be detected by the angular velocity detecting means and the vibration of the first vibrator can be detected independently of the angular velocity by the vibration state monitor, therefore, it is possible to always maintain a constant amplitude of the first vibrator.
According to a second aspect of the invention, the angular velocity detecting means comprises a detection fixed side electrode provided on the substrate and a detection movable side electrode provided for the second vibrator opposite to the detection fixed side electrode, and the vibration-state monitor means comprises a monitor fixed side electrode provided on the substrate and a monitor movable side electrode provided for the first vibrator opposite to the monitor fixed side electrode.
With this configuration, the angular velocity detecting means can detect the displacement in the orthogonal direction of the second vibrator as an electrostatic capacitance between the detection fixed side electrode and the detection movable side electrode. Also, the vibration-state monitor means can detect the displacement of the first vibration in the parallel direction as the electrostatic capacitance between the monitor fixed side electrode and the monitor movable side electrode.
According to a third aspect of the invention, the monitor fixed side electrode of the vibration-state monitor means is integrated with the detection fixed side electrode of the angular velocity detecting means.
With this configuration, a detection signal detected by the angular velocity detecting means and a monitor signal monitored by the vibration-state monitor means can be output from either the detection fixed side electrode or the monitor fixed side electrode. Then, the monitor fixed side electrode of the vibration state monitor means is integrated with the detection fixed side electrode; therefore, it is possible to make the angular velocity sensor smaller than a case in which these are separated.
According to a fourth aspect of the invention, the first support beam is positioned between said substrate and the first vibrator and is provided to support said first vibrator so as to be displaceable in one axial direction (in the X-axis direction) and the second support beam is positioned between the first vibrator and the second vibrator and provided to support the second vibrator so as to be displaceable in a direction orthogonal (in the Y-axis direction) to said one axial direction.
With this configuration, the first support beam supports the first vibrator to be displaceable in the X-axis direction while restricting the first vibrator from being displaced in the Y-axis direction. Also, since the second support beam supports the second vibrator to be displaceable in the Y-axis direction with respect to the first vibrator, the second vibrator is displaced in the X-axis direction together with the first vibrator and is also displaced in the Y-axis direction. Therefore, when an angular velocity around the Z-axis orthogonal to the X-axis and the Y-axis is applied in a state in which the first vibrator and the second vibrator vibrate in the X-axis direction, the second vibrator is displaced in the Y-axis direction due to a Coriolis force; however, the first vibrator is restricted to be displaced in the Y-axis direction. As a result, the vibration-state monitor means provided between the first vibrator and the substrate can detect only the displacement of the first vibrator in the X-axis direction and, therefore, the vibration state of the first vibrator can be detected accurately without being affected by angular velocity or the like.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.